This invention relates to a process for treating liquid hydrocarbons which contain mercaptan compounds.
Mercaptans are malodorous organic sulfur compounds found in varying concentrations in liquid hydrocarbons. There are two basic methods for treating hydrocarbons containing mercaptans: (1) removal of the mercaptans from the hydrocarbon in a process known as extraction; or (2) neutralization of the mercaptans by conversion to disulfides in the hydrocarbon in a process known as sweetening.
In the extraction process, the mercaptan-rich hydrocarbon is combined with an aqueous alkaline solution, typically in a cross-flow vessel such as a vertical tray column. The mercaptans react with the caustic to form water-soluble mercaptides. The mercaptide/alkaline solution is typically regenerated in a separate vessel by oxidation in the presence of a catalyst to convert the mercaptides to disulfide oil. The disulfide oil is then separated from the alkaline solution, and the regenerated alkaline solution is recycled to the extraction vessel. U.S. Pat. No. 3,409,543 and U.S. Pat. No. 4,404,098, the disclosure of which are incorporated herein by reference, describe two such extraction processes.
In the sweetening process, the mercaptan-rich hydrocarbon is oxidized in the presence of a catalyst to convert the mercaptans to disulfides. The disulfides are soluble in the hydrocarbon and remain in solution with the final hydrocarbon product. Thus, while the sweetening process does not reduce the overall sulfur content of the hydrocarbon, it eliminates the offensive mercaptans. This process is therefore suitable for treating hydrocarbons in which some sulfur content is not objectionable. A sweetening process is described in U.S. Pat. No. 2,882,224, the disclosure of which is incorporated herein by reference.
A mercaptan treating process employing both methods is described in U.S. Pat. No. 3,574,093, the disclosure of which is incorporated herein by reference.